Gasoline recovery



' R. B. SMITH GASOLINE RECOVERY Filed Jan. 19, 1938 `lune ll, ,1940.`

gasoline product. volatile hydrocarbons also tends to entail serious` Patented June l1, 1940 PATENT OFFICE 2,204,285 g GAsoLlNE RECOVERY Reading Barlow Smith, Hammond, Ind., assignor to Sinclair Rening Company, New York, N. K a corporation of Maine Application January 19, 193s, serial Naisasic Raw gasoline fractions as originally collected, in both renery practice and field practice, usually include hydrocarbons ranging from normally gaseous hydrocarbons such aspropane and butane through hydrocarbons of boiling point approximating the end point of the gasoline fracV tion. 4 The more volatile constituents ofthe com'- posite increase its vapor pressure and thusgmak'e it unsuitable. as, or as a component of, a nished The presence of these more losses during storage and any further processing, chemical treatment and simple redistillation, of such raw gasoline fractions.

carbons but, through reduction of the partial pressure of those hydrocarbonsboiling near the lowerA end of the range of the desired gasoline product, include .losses of constituents -valuable y as components of the desired gasoline product. For these and related reasons, it` has become conventional practice successively to debutanize and to stabilize the hydrocarbon mixtures constituting such raw gasoline fractions..

In the debutanizing operatiomthe raw gasoline fraction is separated, byfractionation at elevated temperature and under superatmospheric pressure, into a bottoms of limited volatility and an overhead including the more volatile constituents of the raw gasoline fraction.' u This operation' kis frequently controlled so that the butanes, or the greater part of the butanes, present are separated as a component oi the overhead, hence the designation debutanizing l f In the stabilizing operation another gasoline fraction, of vapor pressure higher than that separated as bottoms in the debutanizing operation,

is separated from the extremely volatile components of the debutanizer overhead, by fractionation atv elevated temperature and .under superatmospheric pressure.y The fractionation is controlled to retain inthe liquid gasoline product a maximum proportion ci all constituents higher boiling thanA a` predetermined minimum and to excludel from this product a maximum proper-t tion of lower boiling constituents, to effect a maximum liquid recovery While eliminating Wildness incident to the presence of those con'- stituents of extreme volatility, hence the designation stabilizing, n

The temperatures and pressures maintained in the debutanizing operation are interdependent. From the standpoint of the quality of the less volatile gasoline product, it is important that the maximum temperatures attained in the debutan- Such losses are not i losses merely of these normally gaseous hydro- (cl. 19e-11.)l

izing operation be kept as low as` possible. This maximum temperature is a particularly important factor) if the separated gasoline product is not to be subjected to subsequent chemical treatment and redistillation. vAs the maximum temperature attained in the .debutanizing operation increases, the formation of polymers increases, the gum contentof the gasoline rproduct increases, the end point of the gasoline product increases and the yield oi the gasoline product decreases.

If it be attempted to avoid these adverse eects merely by reducing the maximum temperature attained inthe debutanizing operation,l 'the' proportion of the raw gasoline fraction separated as bottoms increases and that separated as overhead decreases, the vapor pressure of thel bottoms increases, the amount of incondensible lgas produced in the debutanizing operation increases, the amount of gasoline material lost with or requring recovery from this vincreased gasmake increases and theboiling range of the gasoline product recovered by stabilizing this overhead decreases; l l

Similarly, the temperatures attained in the debutanizingoperaton cannot be reduced economically merely by reducing the pressure, thus to reduce the temperature necessary to effect the separation, because such pressure reduction increases the amount of'incondensible gas produced with consequent increase either in the loss of gasoline material in such gas or the expense of recovery of such gasoline material and because such pressure reduction increases the sizeof the equipment required per unit of capacity.

yMy invention provides an improved method-of operation whichV permits .the reductionv of the pressure maintained in the debutanizing opera-V tion, and thus of the maximum temperature necessary to effectl the desired separation, Without increasing the amountoi incondensible gas pro-v duced by the debutanizing operation. I accomplish this result by reducing the vapor pressure of the liquid overhead product of the debutanizing operation by mixingwith it arecirculated partof the liquid product of the stabilizing operation; This recirculated liquid product of the stabilizing operation may 4be admixed with the liquid overhead product from the debutanizing voperation inthe receiver or accumulator into which the condenser for the-debutanizer overhead discharges `or it may bev added to .the .overhead flowing vfrom `the debutani'zer through .this condenser tothe receiver or accumulator. f

An operationembodying my invention is diagrammed in the accompanying drawing, In this product of the combined operation. Overhead from the debutanizer tower 2 passes to the co'n-v denser 6 which discharges into the accumulator "I, The head temperature of the debutanizer tower 2 is. controlled by regulated reintroduction, through connection 8, of condensate from the accumulator 7. The vapor mixture from the accumulator 'I passes to condenser I0 discharging into accumulator I2, the debutanizer accumulator. Incondensible gas accumulating in the accumulator I2 is discharged through connection I3. The raw overhead from the debutanizing operation, separated as a condensate in the accumulator I2, is supplied to the stabilizer tower I5 through heat exchanger I4 and heater I5. The bottoms from the stabilizer tower Iii flow to the kettle I'I in which heat for effecting the stabilizing operation is supplied, by steam for example. Vapors from the kettle are returned to the stabilizer tower I6 and the remaining bottoms passed through heat exchanger I4 and cooler I9. The head temperature of the stabilizer tower I6 is controlled by regulated reintroduction of condensate from the accumulator 20. The gas mixture separating in the accumulator 20 is discharged through connection 24. The liquid product from the stabilizing operation, the bottoms leaving cooler I9, is divided into two parts, one of which moves to storage through connection 25 and the other of which is recirculated to the debutanizer accumulator I2 through connection 2I. This recirculated part of the liquid product of the stabilizing operation may be introduced into the accumulator I2 through connection 2|, 2t and II, or it may with advantage be introduced into this accumulator I2 through connections 2I, 22 and II thus passing through the condenser I0 with the overhead from the debutanizer tower 2. If the recirculated bottoms from the stabilizing operation are passed through the condenser I0, the velocity through, and consequently the heat transfer rate in, the condenser are increased and the additional mixing in the condenser of the debutanizer overhead and the recirculated material assists the operation. The bottoms discharged through connection 25 are the more volatile gasoline product of the combined operation.

The following example will illustrate the operation and the advantages of my invention: In an operation in which a gauge pressure of pounds per square inch and a temperature of 100 F. are maintained on the debutanizer accumulator, the vapor pressure of the liquid collected in this accumulator will approximate pounds per square inch absolute at 100 F, In conventional operation stabilizer bottoms may have, for example, a vapor pressure of 30-36 pounds. per square inch absolute at 100 F. By blending such stabilizer bottoms of lower vapor pressure with the debutanizer overhead of higher vapor pressure, a blend of intermediate vapor pressure is produced. Thus, the debutanizer accumulator can be operated at a correspondingly reduced pressure without increasing the production of incondensible gas in the debutanizing operation. For example, a blend having a vapor pressure of 60 pounds per square inch absolute at 100 F. may be produced by recirculating stabilizer bottoms having a vapor pressure of 30 pounds per square inch absolute at 100 F. at a rate equal to the rate of production of debutanizer overhead, thus permitting reduction of the working pressure maintained on the debutanizer accumulator from say 100 pounds per square inch gauge to 60 pounds per square inch gauge without increasing the gas make. If with operation under a pressure of 100 pounds per square inch a debutanizer kettle temperature, the maximum temperature attained in the debutanizing operation, of 400 F. were necessary, the same separation would be effected with a kettle temperature of only 370 F., for example, by operation under 60 pounds per square inch gauge in accordance with my invention. This reduction of the maximum temperature attained in the debutanizing operation decreases the formation of polymers, decreases the gum content of the gasoline product, avoids increase of the end point of the gasoline product and improves the yield of the gasolinel product. And by means of my invention these important advantages are secured without those offsetting disadvantages incident to temperature, or pressure and temperature, reductions as hitherto proposed.

My invention is also useful to limit, or eliminate, the production of incondensible gas in the debutanizing operation. In this aspect, the pressure maintained in the debutanizing operation may not be increased, but by reducing the vapor pressure of the material collecting in the debutanizer accumulator in accordance with my invention the separation of gas in this accumulator may be minimized.

I claim:

1. In debutanizing and stabilizing gasoline in a system where the raw gasoline fraction is separated in a debutanizer into a liquid bottoms of limited volatility and an overhead vapor fraction which passes through a condenser to an accumulator and in which the condensed overhead fraction from said accumulator is thereafter separated in a stabilizer into a liquid bottoms and an overhead fraction, the improvement which comprises reducing the vapor pressure of the liquid discharged from said condenser for the debutanizer overhead by' admixing therewith a recirculated part of the liquid bottoms from the stabilizer.

2. In debutanizing and stabilizing gasoline in a system where the raw gasoline fraction is separated in a debutanizer into a. liquid bottoms of limited volatility and an overhead vapor fraction which `passes through a condenser to an accumulator and in which the condensed overhead fraction from said Vaccumulator is thereafter separated in a stabilizer into a liquid bottoms and an overhead fraction, the improvement which comprises the reducing the vapor pressure of the liquid discharged from the condenser for the debutanizer overhead by adding a recirculated part of the liquid bottoms from the stabilizer to the debutanizer overhead flowing from the debutanizer through said condenser.

READING BARLOW SMITH. 

